Convergent evolution and parallelism in plant domestication revealed by an expanding archaeological record

Abstract

Recent increases in archaeobotanical evidence offer insights into the processes of plant domestication and agricultural origins, which evolved in parallel in several world regions. Many different crop species underwent convergent evolution and acquired domestication syndrome traits. For a growing number of seed crop species, these traits can be quantified by proxy from archaeological evidence, providing measures of the rates of change during domestication. Among domestication traits, nonshattering cereal ears evolved more quickly in general than seed size. Nevertheless, most domestication traits show similarly slow rates of phenotypic change over several centuries to millennia, and these rates were similar across different regions of origin. Crops reproduced vegetatively, including tubers and many fruit trees, are less easily documented in terms of morphological domestication, but multiple lines of evidence outline some patterns in the development of vegecultural systems across the New World and Old World tropics. Pathways to plant domestication can also be compared in terms of the cultural and economic factors occurring at the start of the process. Whereas agricultural societies have tended to converge on higher population densities and sedentism, in some instances cultivation began among sedentary hunter-gatherers whereas more often it was initiated by mobile societies of hunter-gatherers or herder-gatherers.

Keywords: Neolithic; agriculture; archaeobotany; archaeology; vegeculture.

Fig. 1.

Map of centers of domestication. Black areas indicate key areas of early seed crop domestication and hatched regions have an early focus on vegeculture. Species with quantified domestication rates are indicated, whereas others (species in parentheses) are discussed in the text.

Fig. 2.

Evidence for protracted domestication episodes in Old World cereals, including proportion of nonshattering spikelet scars (Upper) and grain size indices (Lower).

Fig. 3.

Rates of change in domestication traits across the collected dataset. (A) Graph comparing frequency of rates in terms of percentage change in trait per year. (B) Scatter of all haldane rate estimates, indicating trait/crop type. (C) Frequency of estimated selection coefficients in the dataset.